Chip-Scale Atomic Clock (CSAC) improves GPS security

It is hard to imagine modern cars without advanced sensor technology. These "sensory organs" record a wide range of data, such as tire pressure, distance to surrounding objects and acceleration in the event of a collision, in order to trigger the airbag, for example. Sensors play a key role in the field of automated driving in particular. These vehicles are equipped with numerous sensors that precisely record and characterize their surroundings - both on a sunny summer's day and on a rainy night. The combination of a wide variety of sensors already enables almost complete detection of the surroundings.

A test from 2019 showed the serious consequences that disruptions in GNSS communication can have for highly automated vehicles: A Tesla Model S was distracted from the road by manipulated (GNSS spoofing) signals. Quantum sensors offer an efficient way of counteracting these problems. These high-precision sensors can not only work independently of GNSS, but can also detect spoofed GNSS signals and thus offer a reliable alternative. In GNSS spoofing, the receiver is tricked into tuning in to the signal of a so-called spoof instead of the real satellite signal, thereby deflecting it from its true position. Today, such spoofed signals are detected by comparing them with additional sensor data (e.g. LiDAR, radar) and by analyzing the received signal (e.g. unusually high signal strength). In GNSS spoofing, the receiver is tricked into tuning in to the signal of a so-called spoof instead of the real satellite signal, which distracts it from its true position. Today, such spoofed signals are detected by comparing them with additional sensor data (e.g. LiDAR, radar) and by analyzing the received signal (e.g. unusually high signal strength).

Chip-scale atomic clocks (CSACs): a compact, energy-efficient solution for precise time measurement

The use of Chip-Scale Atomic Clocks (CSACs) now brings a new level of security to the system: to pull the receiver away from the real GNSS, spoofer gradually build in small delays which are absorbed by the estimated clock distortion in the receiver. CSACs recognize such clock distortions and thus protect against spoofing.
Another area in which quantum sensors play a decisive role is precise time measurement. This is where chip-scale atomic clocks (CSACs) and compact atomic clocks (CACs) come into play. These devices are further developments of traditional atomic clocks and offer a compact, energy-efficient solution for precise time measurement. Their high accuracy is particularly advantageous for the navigation of autonomous vehicles, as they enable precise time measurement and therefore highly accurate positioning via time-of-flight triangulation.
For global positioning using the usual one-way time-of-flight measurements of GNSS signals, the time scales of the satellites must be synchronized with those of the receiver. Due to the low accuracy of the quartz oscillators installed in the receivers, the clock error in the receiver must be estimated using the coordinates of at least four satellites. The high accuracy of CSACs in conjunction with clock modeling enables precise positioning with only three satellites, which means that GPS positioning is possible, especially in urban canyons and tunnels. This significantly improves the reliability and accuracy of navigation, which is crucial for the safety of vehicles.

Precise laser distance measurements are essential for the local navigation of autonomous vehicles. In this measurement method, a light pulse is emitted, reflected by surrounding objects and then returns to the receiver. By measuring the transit time, the distance to the objects can be determined. The more accurate the time, the more precise the measurement. This technology makes it possible for highly automated vehicles to detect obstacles in real time and navigate safely around them.

CSACs can also be used to enable GNSS-free navigation. In combination with a quantum inertial sensor, the United Kingdom has succeeded in navigating an aircraft entirely without a GPS signal. On the one hand, this enables precise navigation in remote regions, while at the same time making systems robust against GNSS jamming, in which GNSS communication is actively hindered.
Chip-scale atomic clocks (CSACs), with their energy efficiency and compactness, offer great opportunities for more navigation safety in the field of highly automated driving. Their ability to perform precise time measurements and enable GNSS-free navigation makes them a valuable addition to future vehicles. In addition, they increase robustness against GNSS jamming and spoofing, which significantly improves the safety and reliability of autonomous navigation.

However, the cost of CSACs is currently still several thousand euros per component, which limits their broad application. However, as research and development progresses, costs are expected to fall as a result of miniaturization, high integration and production quantities.